Some cable measurments
Mar 7, 2011 at 8:56 AM Post #16 of 31


Quote:
jalo said:
Nick, the problem is inherent in the design of this study, as you decided to do multiple sampling (i.e 10x) you are going to incur inter-measurement variation and other random errors that has to be control for.  So you are forced to use averaging to minimize any random errors.  
 
Correct
 
And unfortunately in this case, the actual variations of the inter and intra value for each cable and between cables may be much smaller than the inter-measurement and random errors
 
Agreed
 
and by doing averaging to adjust for the error, you are destroying the actual value also.
 
However if we can say with some confidence that the inter-cable differences are less than the inter-measurement differences then the cable differences are smaller than the measured differences, i.e the test actually exaggerates the differences between cables. Which is consistent with what other loopback type tests have shown.
 
Actually I think with some cleverer maths it migth still be possible to get an accurate picture as we know the level of random variation for cable A and the level of random variation for cable B, I think it is possible to pick the cable differences out from that if there are any differences between these two levels of variation, sadly my maths is not that good.
 
 
In fact, I really do not think you need to do multiple sampling.  You are right to assume that cables behave more consistent and as such, you could have a single trial design (ABAB) with much longer recordings with multiple sampling points.  
 
My software will only allow 23.8 seconds per sample but it can be sampled at higher frequency i.e up to 32K FFT.
 
 
I'm done anyway but I have a measuring device available if you want to volunteer to extend this study ?
 
 
 
 
 
Click to expand...



 
 
Mar 7, 2011 at 4:01 PM Post #17 of 31


Quote:
nick_charles said:
However if we can say with some confidence that the inter-cable differences are less than the inter-measurement differences then the cable differences are smaller than the measured differences, i.e the test actually exaggerates the differences between cables. Which is consistent with what other loopback type tests have shown.

 

Actually I think with some cleverer maths it migth still be possible to get an accurate picture as we know the level of random variation for cable A and the level of random variation for cable B, I think it is possible to pick the cable differences out from that if there are any differences between these two levels of variation, sadly my maths is not that good.


Nick, you are too humble. If you can do or even just understand the concept of one way ANOVA and FFT, your math is better than the majority of people I knew.  I felt the actual value of the variation in cables is nested in some of the measurements but you are right I believe there is a way to tease out the various values.  I'll think about this more.

 
Click to expand...



 
 
Mar 7, 2011 at 5:26 PM Post #18 of 31
Thinking about the statistics for this, it would be fairly simple to do a non-parametric test on the differences between cables. (I don't think that the measurements meet the requirements for something like ANOVA or even pairwise t-tests.) I'd be happy to do the tests if you want to send me the data.
 
I'll explain the tests and assumptions as part of any analysis, to keep things as transparent as possible.
 
Mar 7, 2011 at 5:58 PM Post #19 of 31
Sounds great, Nick, you should take him up on that offer, wow.
 
Mar 10, 2011 at 5:19 AM Post #20 of 31
Can I ask which A/D converter you used to record the sound back to your PC?
 
Mar 10, 2011 at 8:46 AM Post #21 of 31


 
Quote:
hearmotion said:
Can I ask which A/D converter you used to record the sound back to your PC?
Click to expand...


For the first tests I used the Edirol UA-1EX but later it turned out that the $29 Behringer UCA202 was far far far far more linear at lower levels and had lower noise levels and was more consistent across trials, and so the later tests used that. From what I can make out the A/D process (UCA202) was accurate to about 16 bits (based on the measured noise with digital silence) but I am hoping someone here who owns a Behringer can at some point test the AD process more formally
wink.gif

 
I kept debating getting a better ADC but I needed one that had USB, RCA analog inputs,, works with a Wintel machine and was measurably substantially better and I simply could not find one at a manageable price.
 
 
Mar 10, 2011 at 10:57 PM Post #22 of 31
Ah you are now at the opposite end of the game. Just as there are multi thousand dollar D/A converters discussed on this site, so too are A/D converters. Its been a long while since I was in the business of recommending an A/D to anyone. Head over to gearslutz and see what the FOTM is there...
A Berry UCA202 is kinda satiscraptory though. There must be something more accurate slightly further up the price/value scale. 

 
Quote:
nick_charles said:
I kept debating getting a better ADC but I needed one that had USB, RCA analog inputs,, works with a Wintel machine and was measurably substantially better and I simply could not find one at a manageable price.
 
Click to expand...



 
 
Mar 11, 2011 at 2:48 PM Post #23 of 31


Quote:
hearmotion said:
A Berry UCA202 is kinda satiscraptory though. There must be something more accurate slightly further up the price/value scale. 

Sadly no, there is not , the Edirol is 3x the price (and is worse) and the nearest affordable option I found at $150 was discontinued and that was only marginally better and not verifiably so, the Behringer performs  much better than it should do in terms of residual noise and linearity. My needs were quite speficic, it had to have USB and it had to have RCA analog inputs. Most other recorders have TRS connections, but since the RCA plug is a fundamental part of the cable under test I could not bodge around this.


 
Click to expand...



 
 
Mar 18, 2011 at 10:44 AM Post #25 of 31


Quote:
tstewart422 said:
Great work, Nick!
 
Now, do the same with competent amps/DACs and we may convert a few more people to our cause!
Click to expand...



 
Please do not think I have an agenda beyond questioning what is real and what is imaginary, though I consider myself a skeptic we have seen that DBTs show that DACS in circuit  may be different, nwavguy's experiements allowed others to DBT samples from different DACs and in at least two cases members were able to DBT different DACs. If you have been following that thread download the samples and run them through Audacity and plot the Spectra, export it to Excel and chart it, the DACS are quite noticeably different which did surprise me. At first glance they look very similar but there are deviations between DACS of 3 to 5 db at points. The point being that the differences can be measured and do not need to be imagined. The corollary of this is that many people (self included) were unable to DBT the samples, samples that differed by up to 5db which is quite a lot, interesting.
 
True, tests from Spanish site matrixhifi showed audiophile listeners unable to distinguish between $12000 CD players and $200 DVD players or between boutique set-up and low end kit , or between a Benchmark DAC and a Behringer DAC, but everything has to be judged on a case by case basis.
 
That said I would be very surprised if anyone can DBT two normal cables.
 
Nick
 
Mar 19, 2011 at 9:49 AM Post #27 of 31
Quote:
nick_charles said:
Please do not think I have an agenda beyond questioning what is real and what is imaginary, though I consider myself a skeptic we have seen that DBTs show that DACS in circuit  may be different, nwavguy's experiements allowed others to DBT samples from different DACs and in at least two cases members were able to DBT different DACs. If you have been following that thread download the samples and run them through Audacity and plot the Spectra, export it to Excel and chart it, the DACS are quite noticeably different which did surprise me. At first glance they look very similar but there are deviations between DACS of 3 to 5 db at points. The point being that the differences can be measured and do not need to be imagined. The corollary of this is that many people (self included) were unable to DBT the samples, samples that differed by up to 5db which is quite a lot, interesting.
 
True, tests from Spanish site matrixhifi showed audiophile listeners unable to distinguish between $12000 CD players and $200 DVD players or between boutique set-up and low end kit , or between a Benchmark DAC and a Behringer DAC, but everything has to be judged on a case by case basis.
 
That said I would be very surprised if anyone can DBT two normal cables.
 
Nick
Click to expand...

Well, that just puts a bee in my bonnet. And I thought I was doing good with my EMU0404. You mean it's possible that it's NOT razor flat? Crap.
 
Mar 19, 2011 at 11:26 AM Post #28 of 31
You're talking about impedance interactions between amp and headphones, right?  Or did you do a DAC output sample-by-sample comparison without taking phase shift into account?
 
Mar 19, 2011 at 11:34 AM Post #29 of 31
You must log in or register to reply here.

Users who are viewing this thread

Total: 2 (members: 0, guests: 2)
Back
Top